Automatic microfluidic platform for cell separation and nucleus collection

Characterization and Separation of Live and Dead Yeast Cells Using CMOS-Based DEP Microfluidics

This study aims at developing a miniaturized CMOS integrated silicon-based microfluidic system, compatible with a standard CMOS process, to enable the characterization, and separation of live and dead yeast cells (as model bio-particle organisms) in a cell mixture using the DEP technique. DEP offers excellent benefits in terms of cost, operational power, and especially easy electrode integration with the CMOS architecture, and requiring label-free sample preparation. This can increase the likeliness of using DEP in practical settings. In this work the DEP force was generated using an interdigitated electrode arrays (IDEs) placed on the bottom of a CMOS-based silicon microfluidic channel. This system was primarily used for the immobilization of yeast cells using DEP. This study validated the system for cell separation applications based on the distinct responses of live and dead cells and their surrounding media. The findings confirmed the device’s capability for efficient, rapid and selective cell separation. The viability of this CMOS embedded microfluidic for dielectrophoretic cell manipulation applications and compatibility of the dielectrophoretic structure with CMOS production line and electronics, enabling its future commercially mass production.

Micro- and Nano-Devices for Studying Subcellular Biology

Cells are complex machines whose behaviors arise from their internal collection of dynamically interacting organelles, supramolecular complexes, and cytoplasmic chemicals. The current understanding of the nature by which subcellular biology produces cell-level behaviors is limited by the technological hurdle of measuring the large number (>103 ) of small-sized (<1 μm) heterogeneous organelles and subcellular structures found within each cell. In this review, the emergence of a suite of micro- and nano-technologies for studying intracellular biology on the scale of organelles is described. Devices that use microfluidic and microelectronic components for 1) extracting and isolating subcellular structures from cells and lysate; 2) analyzing the physiology of individual organelles; and 3) recreating subcellular assembly and functions in vitro, are described. The authors envision that the continued development of single organelle technologies and analyses will serve as a foundation for organelle systems biology and will allow new insight into fundamental and clinically relevant biological questions.

Active Particle Based Selective Transport and Release of Cell Organelles and Mechanical Probing of a Single Nucleus

Self-propelling micromotors are emerging as a promising microscale tool for single-cell analysis. The authors have recently shown that the field gradients necessary to manipulate matter via dielectrophoresis can be induced at the surface of a polarizable active ("self-propelling") metallo-dielectric Janus particle (JP) under an externally applied electric field, acting essentially as a mobile floating microelectrode. Here, the application of the mobile floating microelectrode to trap and transport cell organelles in a selective and releasable manner is successfully extended. This selectivity is driven by the different dielectrophoretic (DEP) potential wells on the JP surface that is controlled by the frequency of the electric field, along with the hydrodynamic shearing and size of the trapped organelles. Such selective and directed loading enables purification of targeted organelles of interest from a mixed biological sample while their dynamic release enables their harvesting for further analysis such as gene/RNA sequencing or proteomics. Moreover, the electro-deformation of the trapped nucleus is shown to be in correlation with the DEP force and hence, can act as a promising label-free biomechanical marker. Hence, the active carrier constitutes an important and novel ex vivo platform for manipulation and mechanical probing of subcellular components of potential for single cell analysis.

A Disposable Passive Microfluidic Device for Cell Culturing

In this work, a disposable passive microfluidic device for cell culturing that does not require any additional/external pressure sources is introduced. By regulating the height of fluidic columns and the aperture and closure of the source wells, the device can provide different media and/or drug flows, thereby allowing different flow patterns with respect to time. The device is made of two Polymethylmethacrylate (PMMA) layers fabricated by micro-milling and solvent assisted bonding and allows us to ensure a flow rate of 18.6 μl/ℎ - 7%/day, due to a decrease of the fluid height while the liquid is driven from the reservoirs into the channels. Simulations and experiments were conducted to characterize flows and diffusion in the culture chamber. Melanoma tumor cells were used to test the device and carry out cell culturing experiments for 48 hours. Moreover, HeLa, Jurkat, A549 and HEK293T cell lines were cultivated successfully inside the microfluidic device for 72 hours.

Tunable Droplet Manipulation and Characterization by ac-DEP

A novel ac-dielectrophoretic (DEP) device for tunable manipulation and characterization of particles and droplets is presented in this work. To induce DEP forces, the ac electric field is applied via two embedded microelectrodes to generate a local nonuniform electric field perpendicular to the channel length through a pair of asymmetric orifices on the opposite microchannel walls. The droplets experience the DEP effects only when passing through the vicinity of the small orifice, where the strongest gradient of the nonuniform electric field exists. In this study, the ac-DEP manipulation of the particles in the microchannel under different strengths of electrical field was demonstrated first. Then, the separation of particles by size, separation of mixtures of ionic liquid (IL) droplets and oil droplets with the same size by types, and movement of the particles and IL droplets with different frequencies of the applied ac electric field were investigated, respectively. The experimental results match well with the theoretical simulation. In addition, the lateral migration of an IL droplet as a function of the ac frequency was measured, which shows a trend similar to the corresponding Clausius-Mossotti factor. The experimental results demonstrate that with this method, the separation of target particles/droplets with specific size and type can be accomplished by simply adjusting the strength and the frequency of the ac field applied to the microchannels. This paper, for the first time, measured the ac-DEP lateral migration of the particles and IL-in-water emulsion droplets varying with the frequency of the applied ac electric field in the microfluidic chip, providing a method to identify the critical frequency of the droplet and the fingerprint to characterize the droplet.

Portable visual quantitative detection of aflatoxin B1 using a target-responsive hydrogel and a distance-readout microfluidic chip

Aflatoxin B1 (AFB1), as the secondary metabolite of molds, is the most predominant and toxic mycotoxin that seriously threatens the health of humans and animals. In this work, an AFB1-responsive hydrogel was synthesized for highly sensitive and portable detection of AFB1. The AFB1-responsive hydrogel was prepared using an AFB1 aptamer and its two short complementary DNA strands as cross-linkers. For visual detection of AFB1, the hydrogel is preloaded with gold nanoparticles (AuNPs). Upon introduction of AFB1, the AFB1 aptamer binds with AFB1, leading to the disruption of the hydrogel and release of the AuNPs with a distinct color change of the supernatant from colorless to red. In order to lower the detection limit and extend the method to quantitative analysis, a distance-readout volumetric bar chart chip (V-chip) was combined with an AFB1-responsive hydrogel preloaded with platinum nanoparticles (PtNPs). In the presence of AFB1, the hydrogel collapses and releases PtNPs which can catalyze the decomposition of H2O2 to generate O2. The increasing gas pressure moves a red ink bar in the V-chip and provides a quantitative relationship between the distance and the concentration of AFB1. The method was applied for detection of AFB1 in beer, with a detection limit of 1.77 nM (0.55 ppb) where an immunoaffinity column (IAC) of AFB1 was used to cleanup and pre-concentrate the sample, which satisfies the testing requirement of 2.0 ppb set by the European Union. The combination of an AFB1-responsive hydrogel with a distance-based readout V-chip offers a user-friendly POCT device, which has great potential for rapid, portable, selective, and quantitative detection of AFB1 in real samples to ensure food safety and avoid subsequent economic losses.

Organ-Tumor-on-a-Chip for Chemosensitivity Assay: A Critical Review

With a mortality rate over 580,000 per year, cancer is still one of the leading causes of death worldwide. However, the emerging field of microfluidics can potentially shed light on this puzzling disease. Unique characteristics of microfluidic chips (also known as micro-total analysis system) make them excellent candidates for biological applications. The ex vivo approach of tumor-on-a-chip is becoming an indispensable part of personalized medicine and can replace in vivo animal testing as well as conventional in vitro methods. In tumor-on-a-chip, the complex three-dimensional (3D) nature of malignant tumor is co-cultured on a microfluidic chip and high throughput screening tools to evaluate the efficacy of anticancer drugs are integrated on the same chip. In this article, we critically review the cutting edge advances in this field and mainly categorize each tumor-on-a-chip work based on its primary organ. Specifically, design, fabrication and characterization of tumor microenvironment; cell culture technique; transferring mechanism of cultured cells into the microchip; concentration gradient generators for drug delivery; in vitro screening assays of drug efficacy; and pros and cons of each microfluidic platform used in the recent literature will be discussed separately for the tumor of following organs: (1) Lung; (2) Bone marrow; (3) Brain; (4) Breast; (5) Urinary system (kidney, bladder and prostate); (6) Intestine; and (7) Liver. By comparing these microchips, we intend to demonstrate the unique design considerations of each tumor-on-a-chip based on primary organ, e.g., how microfluidic platform of lung-tumor-on-a-chip may differ from liver-tumor-on-a-chip. In addition, the importance of heart–liver–intestine co-culture with microvasculature in tumor-on-a-chip devices for in vitro chemosensitivity assay will be discussed. Such system would be able to completely evaluate the absorption, distribution, metabolism, excretion and toxicity (ADMET) of anticancer drugs and more realistically recapitulate tumor in vivo-like microenvironment.

Analysing calcium signalling of cells under high shear flows using discontinuous dielectrophoresis

Immobilisation of cells is an important feature of many cellular assays, as it enables the physical/chemical stimulation of cells; whilst, monitoring cellular processes using microscopic techniques. Current approaches for immobilising cells, however, are hampered by time-consuming processes, the need for specific antibodies or coatings, and adverse effects on cell integrity. Here, we present a dielectrophoresis-based approach for the robust immobilisation of cells, and analysis of their responses under high shear flows. This approach is quick and label-free, and more importantly, minimises the adverse effects of electric field on the cell integrity, by activating the field for a short duration of 120 s, just long enough to immobilise the cells, after which cell culture media (such as HEPES) is flushed through the platform. In optimal conditions, at least 90% of the cells remained stably immobilised, when exposed to a shear stress of 63 dyn/cm². This approach was used to examine the shear-induced calcium signalling of HEK-293 cells expressing a mechanosensitive ion channel, transient receptor potential vaniloid type 4 (TRPV4), when exposed to the full physiological range of shear stress.

Dielectrophoretic isolation of cells using 3D microelectrodes featuring castellated blocks

We present 3D microelectrodes featuring castellated blocks for dielectrophoretically isolating cells. These electrodes provide a more effective dielectrophoretic force field than thin-film surface electrodes and yet immobilize cells near stagnation points across a parabolic flow profile for enhanced cell viability and separation efficiency. Unlike known volumetric electrodes with linear profiles, the electrodes with structural variations introduced along their depth scale are versatile for constructing monolithic structures with readily integrated fluidic paths. This is exemplified here in the design of an interdigitated comb array wherein electrodes with castellated surfaces serve as building blocks and form digits with an array of fluidic pores. Activation of the design with low-voltage oscillations (±5 Vp, 400 kHz) is found adequate for retaining most viable cells (90.2% ± 3.5%) while removing nonviable cells (88.5% ± 5%) at an increased throughput (5 × 10(5) cells h(-1)). The electrodes, despite their intricate profile, are structured into single-crystal silicon through a self-aligned etching process without a precision layer-by-layer assembly.

Microfluidic devices for the isolation of circulating rare cells: a focus on affinity-based, dielectrophoresis, and hydrophoresis

Circulating rare cells have attracted interest because they can be good indicators of various types of diseases. For example, enumeration of circulating tumor cells is used for cancer diagnosis and prognosis, while DNA analysis or enumeration of nucleated red blood cells is useful for prenatal diagnosis or hypoxic anemia, and that of circulating stem cells to diagnose cancer metastasis. Isolation of these cells and their downstream analyses can provide significant information such as the origin and characteristics of a disease. Novel approaches based on microfluidics have many advantages, including the continuous process and integration with other components for analysis. For these reasons, a variety of microfluidic devices have been developed to isolate and characterize rare cells. In this article, we review several microfluidic devices, with a focus on affinity-based isolation (e.g. antigen-antibody reaction) and label-free separation (DEP and hydrophoresis).

Microfluidic systems for diagnostic applications: a review

Because of intensive developments in recent years, the microfluidic system has become a powerful tool for biological analysis. Entire analytic protocols including sample pretreatment, sample/reagent manipulation, separation, reaction, and detection can be integrated into a single chip platform. A lot of demonstrations on the diagnostic applications related to genes, proteins, and cells have been reported because of their advantages associated with miniaturization, automation, sensitivity, and specificity. The aim of this article is to review recent developments in microfluidic systems for diagnostic applications. Based on the categories of various fluid-manipulating mechanisms and biological detection approaches, in-depth discussion of the microfluidic-based diagnostic systems is provided. Moreover, a brief discussion on materials and manufacturing techniques will be included. The current excellent integration of microfluidic systems and diagnostic applications suggests a solid foundation for the development of practical point-of-care devices.

Evaluation of a centrifuged double Y-shape microfluidic platform for simple continuous cell environment exchange

We have demonstrated the efficacy of a microfluidic medium exchange method for single cells using passive centrifugal force of a rotating microfluidic-chip based platform. At the boundary of two laminar flows at the gathering area of two microfluidic pathways in a Y-shape, the cells were successfully transported from one laminar flow to the other, without mixing the two microfluidic mediums of the two laminar flows during cell transportation, within 5 s with 1 g (150 rpm) to 36.3 g (900 rpm) acceleration, with 93.5% efficiency. The results indicate that this is one of the most simple and precise tools for exchanging medium in the shortest amount of time.

Manipulation of micro-particles by flexible polymer-based optically-induced dielectrophoretic devices

This study presents a novel technology to manipulate micro-particles with the assistance from flexible polymer-based optically-induced dielectrophoretic (ODEP) devices. Bending the flexible ODEP devices downwards or upwards to create convex or concave curvatures, respectively, enables the more effective separation or collection of micro-particles with different diameters. The travel distances of the polystyrene beads of 40 μm diameter, as induced by the projected light in a given time period was increased by ~100%, which were 43.0 ± 5.0 and 84.6 ± 4.0 μm for flat and convex ODEP devices, respectively. A rapid separation or collection of micro-particles can be achieved with the assistance of gravity because the falling polystyrene beads followed the inclination of the downward and upward bent ODEP devices.

On-Chip Particle Sorting into Multiple Channels by Magnetically Driven Microtools

This paper presents a new type of sorting system by magnetic microtools (MMT) separating particles into multiple channels. Two nickel-based MMTs are activated by commercially available permanent magnets below the biochip to lead particles to certain channels via fluid force. The horizontally assembled permanent magnet drive we developed shows that the MMT positioning accuracy had been improved 5 times in 2 degrees of freedom. The channel and the MMT shape are determined based on FEM analysis to ensure that particles flow smoothly. We have successfully achieved to sort 100 µm diameter microbeads into 7 branched channels. The noncontact drive and disposable chip provide a less invasive environment for the cell with low cost.

Rare Cell Capture in Microfluidic Devices

This article reviews existing methods for the isolation, fractionation, or capture of rare cells in microfluidic devices. Rare cell capture devices face the challenge of maintaining the efficiency standard of traditional bulk separation methods such as flow cytometers and immunomagnetic separators while requiring very high purity of the target cell population, which is typically already at very low starting concentrations. Two major classifications of rare cell capture approaches are covered: (1) non-electrokinetic methods (e.g., immobilization via antibody or aptamer chemistry, size-based sorting, and sheath flow and streamline sorting) are discussed for applications using blood cells, cancer cells, and other mammalian cells, and (2) electrokinetic (primarily dielectrophoretic) methods using both electrode-based and insulative geometries are presented with a view towards pathogen detection, blood fractionation, and cancer cell isolation. The included methods were evaluated based on performance criteria including cell type modeled and used, number of steps/stages, cell viability, and enrichment, efficiency, and/or purity. Major areas for improvement are increasing viability and capture efficiency/purity of directly processed biological samples, as a majority of current studies only process spiked cell lines or pre-diluted/lysed samples. Despite these current challenges, multiple advances have been made in the development of devices for rare cell capture and the subsequent elucidation of new biological phenomena; this article serves to highlight this progress as well as the electrokinetic and non-electrokinetic methods that can potentially be combined to improve performance in future studies.

Bulk-heterojunction polymers in optically-induced dielectrophoretic devices for the manipulation of microparticles

This paper presents a decent polymer material for fabricating optically-induced dielectrophoretic (ODEP) devices, which can manipulate microparticles or cells by using moving light patterns. A thin film of a bulk-heterojunction (BHJ) polymer, a mixture of regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester, is used as a light-activated layer. When illuminated by a projected light beam, the photo-induced charge carriers created by the electron transfer of excitons at a donor/acceptor interface in the BHJ layer, disturbs the uniformly-distributed electric field applied on the ODEP devices. A negative DEP force is then generated by virtual electrodes defined by the optical images from a computer-programmable projector to manipulate microparticles, thus providing a functionalized platform for particle manipulation. The effect of the polymer thickness and composition on the magnitude of the generated DEP force has been extensively investigated. The maximum particle drag velocity and the force applied on 20.0 mum diameter polystyrene beads are measured to be approximately 202.2 mum/s and 38.2 pN, respectively, for a device with a 497.3-nm thick BHJ layer. The lifetime of the developed device is also explored (~5 hours), which is sufficient for applications of disposable ODEP devices. Therefore, the BHJ polymer may provide a promising candidate for future ODEP devices capable of nanoparticle and cell manipulation.

Dielectrophoresis for manipulation of micro/nano particles in microfluidic systems

Dielectrophoretic (DEP) force is exerted when a neutral particle is polarized in a non-uniform electric field, and depends on the dielectric properties of the particle and the suspending medium. The integration of DEP and microfluidic systems offers numerous applications for the separation, trapping, assembling, transportation, and characterization of micro/nano particles. This article reviews the applications of DEP forces in microfluidic systems. It presents the theory of dielectrophoresis, different configurations, and the applications of such systems for particle manipulation and device fabrication.